Re: Little annoying mistakes ... of others

[toolic]

A pretty common logic error is forgetting to explicitly check all expected values against the variable:

use strict;
use warnings;

my $foo = 'boo';
if ($foo eq 'goo' || 'moo') {
    print "$foo\n";
}

when this is really desired:

if ($foo eq 'goo' || $foo eq 'moo') {

Obviously, this is not unique to Perl, but I do see it quite often.

[jeffa]

Actually ... i would desire this:

use strict;
use warnings;

my $arg   = shift || 'boo';
my @valid = qw( goo moo foo voo doo poo );

print "$arg matches\n" if grep /$arg/, @valid;

But this bring up an annoyance as well, because this mistake will compile and always return true (as long as the array being checked is not empty):

# wrong way ahead!
print "$arg matches\n" if grep $arg, @valid;

Oops!

[szabgab]

Wow, I am writing down the examples as test cases but I can't figure out why is the second example always true?

could you please explain?

[jeffa]

I think this:

print "$arg matches\n" if grep $arg, @valid;

Is equivalent to this:

print "$arg matches\n" if grep { $arg } @valid;

So as long as @valid and $arg are not false, then the match will also be true. (If $arg is 0 (zero) then the second example will not always be true.)

[szabgab]

This is exactly the type of examples I am looking for.

Funny as I have just seen this happen in my last class 4 days ago.

[parv]

if ($foo eq 'goo' || 'moo') { ... }

Error that may be but I do wish somethimes that that ought to be correct.

[szabgab]

goto Perl 6;